Along with the miniaturization of a semiconductor integrated circuit and high integration, improvements in resolution are demanded in a projection exposure tool for manufacturing. In order to meet the demands, the wavelength of the light source for exposure is shortened, and, the extreme ultraviolet radiation source device (hereinafter referred to as an EUV (Extreme Ultra Violet) light source apparatus) which emits extreme ultraviolet radiation (hereinafter referred to as EUV light) with the wavelength in a range of 13-14 nm, especially the wavelength of 13.5 nm, has been developed as a semiconductor exposure light source for the next generation thereof, following an excimer laser device.
Although some methods of generating EUV light in such a EUV light source device are known, in one of these methods, high temperature plasma is generated to take out the EUV light emitted from this plasma by heating and exciting a substance (EUV radiating species) which emits extreme ultraviolet radiation. Such EUV light source devices are roughly divided into a LPP (Laser Produced Plasma) system and a DPP (Discharge Produced Plasma) system according to high temperature plasma generation types. The LPP EUV light source device generates high temperature plasma by laser ablation, and, on the other hand, the DPP EUV light source device generates high temperature plasma by current drive.
As types of electric discharge in the DPP EUV light source device, there are a Z pinch discharge, a capillary electric discharge, a plasma focus discharge, a hollow cathode triggered Z pinch discharge, etc. The DPP system has advantages of miniaturization of a light source apparatus and small power consumption in a light source system, so that practical application of a DPP system is also greatly expected, as compared with a LPP system.
In the EUV light source devices according to the both systems, although (around) 10-valent xenon (Xe) ion is known as the radiating species which emits EUV light with a wavelength of 13.5 nm, i.e., material of high temperature plasma, lithium (Li) ion and tin (Sn) ion are attracted attention as materials for obtaining higher radiant intensity. Among these, since the EUV conversion efficiency (=the optical output/electric input) of tin, i.e., the ratio of an EUV light output with a wavelength of 13.5 nm to an electric input required for generation of high temperature plasma, is several times as large as that of xenon, tin is regarded as a highly possible radiation species of mass-produced type EUV light source.
For example, an extreme ultraviolet radiation light source using a gas-like tin compound (for example, stannane gas: SnH4 gas) is disclosed in Japanese Laid Open Patent No. 2004-279246. Moreover, an extreme ultraviolet radiation light source in which liquid-like tin is supplied to a rotating electrode is disclosed in International Publication No. WO2005/025280.
Furthermore, Japanese Laid Open Patent (Tokuhyo) No. 2004-501491 discloses a structure in which buffer gas is introduced in a light source of extreme ultraviolet radiation from a light emitting side of a collector unit, and the gas is passed through the collector unit, and exhausted from the light incidence side.
As in Japanese Laid Open Patent (Tokuhyo) No. 2004-501491, FIG. 13 shows a flow of buffer gas in an extreme ultraviolet radiation light source in which buffer gas is introduced from the light emitting side of a collector unit and exhausted from the light incidence side. In FIG. 13, when electric power is supplied between a first electrode 11 and a second electrode 12 and pulsed large current flows between the first electrode 11 and the second electrode 12, high temperature plasma P occurs by Joule heating due to the pinch effect, so that EUV light is emitted from the high temperature plasma P. The generated EUV light is emitted from an EUV light extraction section 7 through a collector unit 2 arranged in a second chamber 10b. A gas curtain nozzle 4 which is connected to a gas supply unit 16a, and a first gas exhaust unit 9a are provided in an area between an electric discharge section 1 and the collector unit 2, and a second gas supply unit 16b is provided in a light emitting side of the collector unit 2. And gas supplied from the second gas supply unit 16b is exhausted from the first gas exhaust unit 9a through the circumference thereof and the inner side of the collector unit 2.